Geoscience Reference
In-Depth Information
Fig. 2.43
Scheme of geological, tectonic and hydrogeological
features of Bosnek Karst Region (after Benderev and Shanov
1997
) 1—Lower Triassic sandstones (T
1
); 2—Anisian lime-
stones (T
a
); 3—Ladinian dolomites (T
l
); 4—Ladinian shales
(T
l
);
8—Siltstones and marls (Tithonian—J
3
); 9—Senonian volcanic
rocks of Vitosha Mountain (K
s
); 10—Quaternary sediments;
11—fault; 12—normal fault; 13—thrust; 14—cave entrance;
15—karst spring; 16—principal direction of underground water
flow; 17—site of investigations of the rock fracturing
(T
k
);
5—Carnian
limestones
6—Dolomites
(Carnian-
Norian—T
k - n
);
(Carnian-Norian—T
k - n
);
7—Limestones
well as at the zones of the faults inter-crossing eastof
the village of Bosnek. Two karst springs, situated in
the northern part of Bosnek, disgorge their water
again into the river of Struma (Fig.
2.43
).
Exactly between the places of water losses and the
springs near the village of Bosnek, the longest cave in
Bulgaria named Duhlata is situated, with total galleries
length over 17 km. Our studies on the tectonic stress
fields and their impact on the hydrogeological pecu-
liarities of the area (Benderev and Shanov
1997
)have
shown that tectonic stress fields created during the
geological history systems of fractures, controlling the
underground waters in the processes of karst formation.
The boundaries of Triassic carbonate complexes,
are commonly tectonic that is predestined by the
structural position of the discussed area. Orogenic
processes and the related karst evolution are con-
trolled by Pernik Fault Zone (Bonchev
1961
,
1971
;
Kostadinov
1965
; Matova and Angelova
1994
) during
Quaternary. Most of the faults crossing the area are
practically segments of this zone with general strike
NW-SE. Tectonic processes caused macro- and
micro-block differential movements and fracturing of
the rocks, leading to the formation of the contempo-
rary valley of Struma River, as well as dividing the
underground catchment, basins and formation of cave
systems (Benderev and Shanov
1997
). The processes
of present day tectonic activity continue, and this is
reflected by the swarm of seismic activity at 20 km
northwestwards of the region during 2012 (Radulov
et al.
2012
), the strongest earthquake being of mag-
nitude M = 5.4.
Karst Evolution
The investigated area was a part of Pernik basin
during the Paleogene and was filled with sediments of
